Gov. Jerry Brown argued the early release would jeopardize public safety.

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The Supreme Court refused Friday to delay a court order for California to release nearly 10,000 inmates by year's end.

The Supreme Court refused Friday to delay a court order for California to release nearly 10,000 inmates by year's end to improve conditions in state prisons, rejecting a request from the governor's office to give the state more time to appeal the order.

The ruling stems from a 5-4 decision in 2011 and a lower court order two years earlier that the state must cut its inmate population to deal with unconstitutional prison conditions caused by overcrowding. On Friday, the court voted 6-3 to reject a plea from Gov. Jerry Brown, who argued the early release would jeopardize public safety.

The order issued Friday did not include an explanation regarding the decision.

Justices Samuel Alito, Antonin Scalia and Clarence Thomas said they would have granted the state's request. They called the lower court's order a "terrible injunction."

Scalia's dissent included a condemnation of what he called "the power of the Black Robe."

The state argued that the inmate release would free thousands of inmates, including violent offenders. Officials had asked the court for more time to challenge the order on appeal.

In the state's July 22 filing, officials claimed conditions have improved since the 2009 order, which called for the prison population to be cut to about 110,000 inmates. Scalia agreed, writing that the state made "meaningful progress" and that such reductions in the inmate population are no longer necessary.

Less dangerous criminals are already being sent to county jails or have been released from state prison, according to the Brown request. Officials said the state has fewer than 1,800 inmates considered low-risk who have not committed felonies in prison or do not have gang affiliations.

More than half of the decrease that has occurred so far is due to a two-year-old state law -- referred to as realignment. The policy sentences offenders convicted of crimes considered non-violent, non-serious and non-sexual to county jails instead of state prisons.

Meeting the demand to release 10,000 inmates would require the release of violent criminals, according to the state.

"No data suggests that a sudden release of inmates with these characteristics can be done safely," the state said in its filing. "No expert has recommended doing it. No state has ever done it."

Medical and mental health care improvements are at the core of the court order.

The state is spending $2 billion on new or expanded facilities for inmate medical and mental health treatment. That includes seven new centers for mental health treatment and the opening last June of an $839 million prison hospital in Stockton that will treat 1,722 inmates requiring long-term care.

The state also has boosted hiring and salaries for all types of medical and mental health professionals.

The panel of judges that handed down the order four years ago has gone so far as to threaten the governor for contempt if California does not comply.

The judges waived all state laws in June as they ordered Brown to expand good-time credits leading to early release. They also directed the governor to take other steps, including sending more inmates to firefighting camps, paroling elderly felons, leasing cells at county jails and slowing the return of thousands of inmates now housed in private prisons in other states.

If those steps fail, the judges ordered the state to release enough inmates from a list of lower-risk offenders until it reaches the maximum allowed population.

The ruling comes on the same day California's prison chief agreed to meet with advocates for inmates who are on a hunger strike to protest the state's solitary confinement program. Corrections Secretary Jeffrey Beard will meet Friday afternoon with members of a coalition supporting more than 300 inmates who have refused all meals since July 8.

The protesters are demanding an end to indeterminate sentences in isolation units. They also want alternative ways to leave the units.